This invention relates to rolling mill control systems. More particularly, it relates to a system for controlling the diametric dimensions of a round bar in the finishing stands of a bar mill.
Automatic control of rolling mills is broadly old, particularly insofar as the rolling of flat products, e.g., sheet steel, is concerned. In these mills, the thickness dimension of the product is either continuously or periodically measured. The roll gap of one or more stands of the rolling mill is then varied, in accordance with a mathematical relationship, to obtain a product of the desired dimensions.
This same basic control philosophy has been followed in the past in connection with mills for rolling rounds bars. In bar mills, however, changing the roll gap in a stand causes all other dimensions about the periphery of the bar to change, also. This phenomenon has been recognized, and control systems have been devised that measure the diameter of a bar at the roll pass line and also in a direction perpendicular thereto. However, such systems have been unsatisfactory in producing a product of accurate dimensions for several reasons. First, it is quite likely that the maximum and the minimum bar diameters may occur at a point on the bar that does not coincide with the particular diameters measured. Thus, the measured diameters give no valuable information relative to either the maximum or the minimum diameter or the extent of out-of-roundness of the bar. Furthermore, these systems do not satisfactorily account for the fact that changing the roll gap changes the dimensions about the entire periphery of the bar. In addition, these prior art systems do not consider the effect of lengthwise variations in diameter due to such factors as roll eccentricity, finishing temperature variations in the bar, variations in tension control, etc.
It is the object of the present invention to provide an improved system and method for controlling the last two stands of a bar mill whereby bars of more uniform diametric size are produced to closer tolerance specifications.